1. Field of the Invention
The present invention relates to a time delay output apparatus for a circuit breaker, and more particularly, to a time delay output apparatus for a circuit breaker which is capable of preventing a malfunction caused by vibration, by excluding the use of a mass, thereby enhancing the operational reliability.
2. Description of the Background Art
In general, a circuit breaker is an protective electrical device disposed between a power source and a load equipment so as to protect the load equipment and an electrical line from a circuit fault (e.g., a large current due to a short circuit, earth fault, etc.) which may occur in an electrical circuit.
Some circuit breakers are provided with a relay performing an MCR (Making Current Release) function, which sets a current value, detects the introduced current, and instantaneously opens the circuit breaker when a large current greater than a reference value is introduced, thus to prevent the flow of the large current into the load side.
The relay blocks the electrical line within a preset allowable delay time. When the circuit breaker is closed to check whether or not a fault occurred in the electrical line, and if the fault is not completely solved, a large fault current flows for the preset allowable time in the electrical line, thereby causing damage in the electrical line and the load. When the circuit breaker is closed to check whether or not a fault occurred in the electrical line, and if a main contact is contacted and thus a fault current is detected, there is a need to instantaneously open the circuit breaker without maintaining the allowable (delay) time preset on the relay in order to reduce damage in the electrical line and the load. Such function is called the “MCR” function.
In order for the relay to perform the MCR function, two cases should be distinguished: one case is where the fault current is blocked (i.e., a fixed contactor and a movable contactor are separated) when the circuit breaker is closed, and another case is where the fault current is blocked (i.e., the fixed contactor and the movable contactor contact each other) when the circuit breaker is closed on an electrical line where the circuit breaker had been opened due to a previously occurred fault. In order to distinguish such two cases, there is provided a time delay output apparatus for a circuit breaker, which outputs a contact signal with a certain delay time after the fixed contactor and the movable contactor contact each other.
As shown in FIGS. 1 and 2, the time delay output apparatus for a circuit breaker includes a switch 20 disposed at one side of a main shaft 10 so as to output a signal when a contact is detected, a delay plate 30 disposed pivotably with respect to a detection portion of the switch 20 so as to contact and be separated from the detection portion of the switch 20, and a lever 12 integrally formed with the main shaft 10, and pressing and pivoting the delay plate 30 so as to be separated from the switch 20 when the main shaft 10 is rotated in an opening direction.
The delay plate 30 includes a pivot shaft 31, a first arm 33 extending from the pivot shaft 31 to the main shaft 10 and contacting the lever 12, and a second arm 35 extending from the pivot shaft 31 to the switch 20 and contacting the detection portion of the switch 20 by being pivoted together with the first arm 33. A spring 37 is connected to the second arm 35 so as to apply an elastic force in a direction urging the second arm 35 to contact the switch 20.
Meanwhile, the second arm 35 is provided with a mass 39 for generating a certain time delay by inertia when the main shaft 10 is rotated in a closing direction.
With such construction, when the circuit breaker is opened, as shown in FIG. 1, the lever 12 presses the delay plate 30, and thus the delay plate 30 is spaced apart from the switch 20. When the main shaft 10 is rotated in a closing direction (i.e., in a counter-clockwise direction in the drawing), the delay plate 30 is pivoted toward the switch 20 in a clockwise direction in the drawing by the urging force of the spring 37. Here, while the delay plate 30 is pivoted, a certain delay is generated by inertia of the mass 39. Such delay serves to output a signal from the switch 20 once the delay plate 30 contacts the detection portion of the switch 20 after the fixed contactor and the movable contactor contact each other by the rotation of the main shaft 10.
However, in this conventional time delay output apparatus for a circuit breaker, a relatively large mass 39 is required to generate a certain (fixed) delay, thereby increasing the size of the time delay output apparatus.
In addition, when a large current is introduced, the inertia when the mass 39 is vibrated or moved by vibration generated by electromagnetic repulsion force becomes more reduced, compared to that of when the mass 39 is stopped. Accordingly, the delay plate 30 cannot maintain the preset delay. Consequently, the switch 20 outputs a signal too early, and the circuit breaker is instantaneously opened, thereby not performing its function properly.